Published byStanford Medicine

The New York Times recently reported on a really interesting treatment for tinnitus, the irritating (and sometimes crazy-making) ringing in the ears that sometimes accompanies noise-related hearing loss. The article doesn’t mention it, but the treatment seems to me to have parallels to therapies for phantom limb pain, and reinforces new ideas about how the brain works.

The tinnitus treatment involves listening to music in which researchers have removed a one-octave frequency band centered around the frequency of the ringing. Those who listened to this “notched” music for 12 hours a week over the course of a year reported much improvement in their tinnitus.

In phantom limb syndrome, people who have lost a limb report that they still sense the limb’s presence, and often feel intense pain that they cannot get rid of. For instance, some people who have lost their hand report that they feel as if the missing hand is permanently and painfully clenched in a fist that they can’t relax. Neuroscientists think that the brain is used to sensory signals coming from the hand, and that when those signals suddenly cease, the brain supplies its own signals about what the hand is doing. A great article in the New Yorker described a similar phenomenon that causes endless itchiness.

A fairly new therapy for phantom limb pain uses a mirror to trick the brain into thinking it is getting signals from the missing hand: the patient is asked to imagine making the same motions with both hands, with the real hand making those motions in front of a mirror while the reflection seems to show the missing hand making the same motions (kind of like the old “levitating” trick). Regular sessions with the mirror seem to supply enough virtual input from the missing hand that the brain is able to reorganize and let go of its need for input.

It may be that a similar thing is happening with tinnitus: when input from some frequencies is missing due to hearing loss, the brain supplies its own input. With phantom limb syndrome, therapists are tricking the brain into thinking it is getting signals from the missing hand, whereas with tinnitus, therapists may be tricking the brain into thinking that the signals from the missing frequency are gone for a reason – the whole octave is missing. In both cases, supplying an artificial context for the missing signals may then allow the brain to stop supplying its own bothersome signal.

Good question. I imagine that it has to do with the fact that the “sound” of tinnitus is generated in the brain and not the ear, and thus could seem to come from both ears even though one has been damaged. A flaw in one spot in the brain could send erroneous signals to the aural sensory regions in both hemispheres. I’m not sure if anyone has ever pinpointed exactly where tinnitus arises.

There’s a fascinating study by Georgetown University Medical Center examing the possible common cause of phantom pain and Tinnitus, involving a malfunction of the corrective feedback loop connection between the brain’s limbic system and the sensation regulating thalamus: